THE ICE-DAMMED LAKES OF OSSIAN SARSFJELLET (SVALBARD) - THEIR GEOMORPHOLOGY AND SIGNIFICANCE

The tidewater glacier complex of Kongsvegen/Kronebreen, at the head of Kongsfjorden in north-west Spitsbergen, has advanced rapidly several rimes since its Neoglacial maximum. Two such advances, 1869 and 1948, are well constrained in rime and space and are widely interpreted as g lacier surges. During the 1869 advance an ice-dammed lake formed on th e western side of Ossian Sarsfjellet. This ice-dammed lake is associat ed with a thrust moraine complex. Four lake levels are identified, two of which are associated with rock-cut shorelines implying a degree of lake stability. The history of this lake, the nature of the ice darn and its relationship to the thrust moraine complex are discussed. The lake history spanning 28 to 35 years is used to assess the ice-margina l dynamics of the Kongsvegen/Kronrbreen glacier. It is concluded that, contrary to previous suggestions, the rapid advance of this tidewater glacier map simply be an example of a non-climatic ice-marginal fluct uation: of the type common to tidewater glacier, as opposed to a glaci er surge. A second ice-dammed lake, to the east of Ossian Sarsfjellet, formed sometime after 1869 as the ice retreated, and still exists tod ay. This largely supraglacial lake is associated with a very different geomorphological assemblage, which has a poor long-term preservation potential. The geomorphological characteristics of the two lakes on Os sian Sarsfjellet are compared and used to discuss the problems associa ted with the recognition of ice-dammed lakes within the Pleistocene re cord. On the basis of the evidence presented heres ice-dammed lakes ma y be more common during deglaciation than currently suggested.